The invention starts from a circuit arrangement for driving a movable element, especially for driving panes or the like in motor vehicles.
For instance the motor of window closing installations of motor vehicles has to be switched off or switched to reverse run on grounds of safety, when the pane meets an obstacle. This is ensured in known versions in that a power-dependent value, for instance the motor current, is evaluated, whereby the motor is switched off as soon as this power-dependent value exceeds a given threshold value. It became obvious in practice that the motor current which is needed to drive a tight pane may be bigger than that motor current value which is permissible on grounds of safety. Therefore such window closing installations with a static current evaluation do not meet the requirements of the practice.
It has therefore been suggested to evaluate the temporary change of the motor current and to derive from it a switching signal for switching off or changing over the motor. This dynamic current supervision starts from the fact that the current rise is very steep, when the pane meets an obstacle, but that the current rise is essentially smaller because of an increasing friction.
The invention is based on the problem to create a circuit arrangement which reliably switches off the motor with only a slight effort, when the movable element driven by the motor meets an obstacle, whereby it is to be ensured, that the power increase due to normal friction and sudden and short-term tightness of the drive system do not result in a switching-off or changing over of the motor.